USGCRP-sponsored research continues to advance understanding of
the causes, magnitude, and consequences of changes in land cover
and in terrestrial and marine ecosystems. The FY96 edition of Our
Changing Planet included a summary of recent key findings.
Highlights of more recent findings follow:

New understanding has been gained of the contemporary global
carbon cycle through the measurement and analysis of changes in
the atmospheric concentration of oxygen and the ratio of 13C° to
12C°
in atmospheric carbon dioxide. These measurements and analyses
support the hypothesis that terrestrial ecosystems of the mid-latitudes of the
Northern Hemisphere have functioned as a significant
carbon sink (up to about a third of the fossil fuel emissions) in the
first half of the 1990s. Without this sink, the causes of which are not
yet understood, the rate of carbon dioxide accumulation in the
atmosphere would have been even faster.

Large-scale ecosystem modeling efforts are making important
progress. The models being developed are prognostic and can be
used to simulate a range of ecological responses to changes in climate
and the chemical composition of the atmosphere. Among the
responses that can start to be considered are time-dependent
changes in the distribution of terrestrial plant communities across
the globe as climate changes.

Long-term ecosystem-level experiments are now providing evidence
that biodiversity plays a critical role in the carbon and nutrient
cycles of terrestrial ecosystems. In addition, regular measurements
are now being taken that will lead to improved estimates of the
effects of interannual climate variability on carbon exchange
between land ecosystems and the atmosphere. This information can
be used to develop and test process-based ecosystem models that are
important components of the larger Earth system models. These
models are critical research tools in global change science and
assessment, and will benefit greatly from improved representation of
ecosystem processes.

New land-cover data for South America, Southeast Asia, and the
conterminous United States have been released on the World Wide
Web
http://amazon.unh.edu/pathfinder/
and
http://edcwww.cr.usgs.gov/landdaac/. The data were developed
from Landsat products. The new information for South America and
Southeast Asia will facilitate better estimates of rates of
deforestation and of the flux of carbon to the atmosphere associated
with forest clearing. The land-cover data for the conterminous United
States, which have a 1-km resolution, are an important information
base for resource managers working on regional-scale planning.

Recent modeling studies have shown that unusual physical conditions
along the break in the Georges Bank's shelf during the late 1950s and
1960s can be traced to changes in the strength of the cold Labrador
Current. The dynamics of planktonic animal populations on the Bank
are thought to be strongly influenced by biological and physical
events in the surrounding deep basins in the Gulf of Maine, the
offshore slope water, and upstream waters on the Scotian Shelf.
Changes in planktonic populations in turn influence the marine
resource populations of these ecosystems. Scientists are evaluating
the impact of such decadal-scale climate-related events on the
seasonal cycle of heating and cooling that controls water column
structure, local circulation, and plankton dynamics.

Recent studies in the tropical Pacific Ocean indicate that iron, which
is relatively abundant in waters near land, may be the limiting
nutrient in determining primary production of marine life in the blue
waters of the central ocean basins. In a series of field experiments
involving controlled additions of iron salts to surface waters,
scientists documented dramatic plankton blooms and concomitant
draw down of other excess nutrients. These results are encouraging
studies of factors controlling primary production, carbon cycling, and
ocean-climate impacts elsewhere in the world ocean.